Try to add a node to a new cluster setup but it said the node is already joined to a cluster

I have set up a two-node-active-passive cluster for SQL server testing purpose and am ready to create a new cluster for production. So I remove the existing cluster and was trying to create a new one. When I add a node to the cluster, it said the node is joined in a cluster already. When I added the other node, it was succesful. All cluster setup for testing and production is done on the same two nodes and SAN. Here is what I did.
1. I use the 'destroy cluster' feature in the Failover Cluster Management tool to wipe out the cluster I set up for testing.
2. I renamed the computer name for both nodes and using new IP addresses.
3. I checked the active directory and make sure the old computer names for the two nodes are not there.
We only have one cluster setup which I erased so I am quite puzzled about why the Failover Cluster management tool thinks that node is joined to a cluster already. The failover cluster management tool doesn't show any existing cluster setup so it should mean there is no cluster existed. What can I do to make the tool thinks otherwise?
Any pointers on this is very much appreciated. I am using Windows 2008 64 bit version with SQL 2008 std 64 bit version.
Wingman